Method of and an apparatus for controlling edge flare in thermal cutting

ABSTRACT

In a method of and apparatus for thermally cutting a piece of glass along an intended path of cut, a thermal or mechanical means modifies a stress profile at a back edge of the piece of glass along the intended path of cut to eliminate edge flare. A heat source concentrates heat on a major surface of the piece along the intended path of cut, and the thermal or mechanical means places a major surface that faces away from the heat source in compression at the back edge so that a fracture will run along the intended path of cut.

United States Patent 1 1 Michalik [451 June 19, 1973 I METHOD OF AND AN APPARATUS FOR CONTROLLING EDGE FLARE IN THERMAL CUTTING [75] Inventor: Edmund R. Michalik, West Mifflin,

211 Appl. No.: 187,258

Oelkc 225/935 Primary Examiner-Frank T. Yost Attorney-Russell A. Eberly [57] ABSTRACT In a method of and apparatus for thermally cutting a piece of glass along an intended path of cut, a thermal or mechanical means modifies a stress profile at a back 521 US. Cl 225/2 83/935 83/965 edge Piece Ofglass m the intended P of 51 Int. Cl. B26: 3/00, 1526f 3/06 eliminate edge flare- A heat source mummies 58 Field of Search 225/935 96.5 2- heat a i Surface Piece along the intended path of cut, and the thermal or mechanical means places a major surface that faces away from the heat [56] Rbferences Cited source in compression at the back edge so that a frac- UNITED STATES PATENTS ture will run along the intended path of cut.

2,146,373 2/1939 Keier 225/935 15 Claims, 8 Drawing Figures k T 39 i 32 A Dear 225/935 X PATENTEB 3. 739.963

MP1 U I w .6 C MPBESSION l, l, [1/ ll/ TENSION I 8 COMPBESSION COMPRESSION L TENSION METHOD OF AND AN APPARATUS FOR CONTROLLING EDGE FLARE IN THERMAL CUTTING CROSS REFERENCE TO RELATED APPLICATIONS This application is related to U.S. Pat. Applications Ser. No. 66,940 and Ser. No. 66,941, both filed on Aug. 26, 1970, by Terrence A. Dear and assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of and an appara tus for cutting hard ceramics, such as glass, along an intended path of cut.

2. Description of the Prior Art Cutting of glass as the result of applying radiant energy to the glass is well known, as is evidenced by the patents to Campbell et al. (U.S. Pat. No. 1,720,883), Hitner (U.S. Pat. No. 1,777,644), Spinasse (U.S. Pat. No. 1,973,546), Kovacik et al. (U.S. Pat. No. 3,344,968), Hifner (U.S. Pat. No. 3,453,097) and Oelke (U.S. Pat. No. 3,587,950). The abovementioned patents do not address the problem of flare, i.e., the tendency of the cut to deviate, near an end thereof, from the intended or desired path of cut.

SUMMARY OF THE INVENTION In accordance with the present invention, a piece of glass is severed along an intended path of cut that extends from a front edge to a back edge of the piece. The first step of the present invention is to induce an artificial defect, such as an edge nick, in the front edge of the piece at one end of the intended path of cut. A primary source of thermal energy is positioned adjacent to the intended path of cut and activated to concentrate thermal energy along said intended path of cut. A thermal or mechanical means is positioned at the other end of the intended path of cut so that it overlaps the back edge of the piece to modify the stress profile at the back edge so that a major surface of said piece of glass opposite to said primary source of thermal energy is placed in compression at the back edge about the intended path.

The artificial defect is normally an edge nick (fracture-initiation score) approximately one-fourth inch (approximately 6.3 millimeters) to one-half inch (12.6 millimeters) that is applied to the glass by an operator using a hand tool.

The method and apparatus of the present invention can be used on plate glass, float glass, sheet glass and low expansion glass, with edges being produced, in each instance, that are straight, smooth, perpendicular and strong.

The term thermal cutting", as used in this application, includes thermal fracturing and thermal scoring/mechanical-snapping. Thermal fracturing, as used in this application, relates to a method wherein the glass is heated along an intended path of cut so that a tensile stress in excess of approximately 1,000 pounds per square inch (approximately 725 grams per square millimeter) is created at approximately the center of the piece of glass to fracture the glass. Thermalscoring/mechanical-snapping", as used in this application, relates to a method wherein the glass is heated along an intended path of cut to create a thermal score and then snapped mechanically about the thermal score before a tensile stress of 1,000 pounds per square inch is created within the glass. The term thermal score, as used in this application, does not mean a scratch or groove in the glass surface, but rather a condition brought about by heat wherein stresses are created on and about the intended path of cut that extend from one surface to an opposite surface of a sheet of glass.

When used in this application, front edge and back edge refer to edges of the piece of glass being cut with which the intended path of cut intersects. It is understood that the front edge is :not necessarily opposite to the back edge. The front edge contains a frac ture-initiation score and the back edge does not.

At room temperature, the major surfaces of a piece of glass are in compression and the center of the piece is in tension. When heat is concentrated along an intended path of cut on a major surface of the piece, surface compression increases on both this major surface and most of the opposite major surface. In addition, the tensional stresses at the center of the piece also increase. Since glass fails more easily in tension than in compression, a fracture generally runs from the center of the piece to the major surfaces.

US. Application Ser. No. 66,940 discloses a method of and an apparatus for thermally fracturing glass using a non-contacting heat source. U.S. Application Ser. No. 66,941 discloses a method of and an apparatus for severing glass sheets using a non-contact thermalscoring, mechanical-snapping method and apparatus. Both of these applications are pertinent to the present invention in that they illustrate details of a suitable source of thermal energy and its operating ranges and characteristics for the thermal cutting of glass. Rather than repeating all of the details relating to operating ranges and characteristics of the source of thermal energy, its relationship with various pieces of glass, cutting times and speeds, et cetera, the above-mentioned Dear disclosures are incorporated into the present disclosure by reference. Differences between the method and apparatus of the present invention and those of the Dear disclosures will be described.

The above-mentioned Dear applications teach that a fracture-initiation score is placed on a piece of glass at a first end of a desired path of cut, and thermal energy is concentrated on the desired path by a non-contact thermal source. The inventions taught in the abovementioned Dear applications are major steps in glass cutting, but it has now been discovered that an irregular stress profile results at the back edge of the piece of glass about the intended path of cut. To be more specific, the major surface facing away from the thermal source at the back edge of the piece about the intended path of cut is in tension, rather than compression, when the piece is heated along the intended path. Further, this tension is at a maximum approximately one-fourth inch to three-eighths inch from the desired path of cut. A running fracture will seek a path of least resistance, and, in this case, such a path is the maximum tension zone. Therefore, when the cut runs from the center of the piece to this major surface at the back edge, the cut does not run perpendicularly to this major surface. Rather, a sharp protrusion away from the intended path of cut (flare) often results.

According to the present invention, a thermal or a mechanical means modifies the stress profile at the back edge of the piece about the desired path of cut so that the major surface of the piece facing away from the opposite heat source is placed preferably in compression, but, in any case, no greater than approximately 1,000 pounds per square inch in tension, so that a fracture propagates from the center of the piece to its major surfaces, thus eliminating the flare.

DESCRIPTION OF THE DRAWINGS A complete understanding of the invention may be obtained from the foregoing and following description thereof, taken in conjunction with the appended drawings, which are diagrammatic and not to scale, and in which:

FIG. 1 is a perspective view of a piece of glass showing the stress profile that results when the piece of glass is heated along an intended path of cut;

FIG. 2 is a perspective view of the piece of glass after it has been thermally severed;

FIG. 3 is a perspective view of a piece of glass showing how the stress profile may be modified by a stress modification means in accordance with the present invention;

FIG. 4 is a perspective view of the piece of glass in FIG. 3 after it has been thermally severed;

FIG. 5 is a perspective view of an apparatus used to thermally cut a piece of glass which includes a stress modification means;

FIG. 6 is a plan view of the apparatus illustrated in FIG. 5;

FIG. 7 is an elevation view of the apparatus illustrated in FIG. 5; and

FIG. 8 is an end view of the apparatus illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a perspective view of a piece of glass 10 that has been heated along an intended path of cut 12 from above by a source of thermal energy, such as the one illustrated in the abovementioned Dear applications. The piece of glass 10 has been broken away at 14 so that the piece may be viewed through its thickness to show the stress profile of the piece. When viewed through its thickness, piece 10 is in compression at major surfaces 16 and 18 about the intended path 12 and is in tension at the central area 20 about the intended path 12. While the piece of glass has been broken away only at 14 in FIG. 1, the stress profile through the thickness of the piece of glass 10 is similar along the entire length of the intended path of cut 12 except for the area that is immediately adjacent to back edge 22. At the back edge 22, bottom major surface 18 is in tension beneath the intended path of cut 12. This causes the cut to stray from the intended path of cut 12 adjacent to back edge 22. FIG. 2 shows the piece of glass 10 after it has been thermally severed. Note how the cut edge 24 is flared at 26 adjacent to back edge 22. The amount of flare varies, but

it may be as much as approximately one-half inch from the intended path (as indicated at X) and approximately one-half inch from back edge 22 (as indicated at Y).

According to the present invention, stress modification means are placed at the back edge of a piece of glass to alter the stress profile at this trail edge. Referring to FIG. 3, there is shown a piece of glass 30 that has been heated along an intended path of cut 32 on top major surface 34 by a thermal source in the same manner as piece 10, except that a stress modification means has also been used. Piece of glass 30 has been broken at 36 so that the stress profile through the thickness of the glass may be seen. The stress profile of piece 30 is identical with the stress profile of piece 10 except that the stress profile adjacent to back edge 40 of piece 30 differs from the stress profile adjacent to back edge 22 of piece 10. This is due to the stress modification means (hereinafter described) which has. placed the area adjacent to bottom major surface 38 and back edge 40 preferably in compression, but at least less than approximately 1,000 pounds per square inch in tension, about the intended path of cut 32. When piece 30 is severed, the resulting cut edge 40 will be smooth, strong, straight and perpendicular, with no flare, as shown in FIG. 4.

Referring to FIGS. 5 to 8, there is shown an apparatus, including a stress modification means 50, for thermally severing a piece of glass 30. The drawings show piece of glass 30 resting on a primary source of thermal energy 54, such as the infrared line heater described in the above-mentioned Dear applications, and a scissors lift 56. The primary source of thermal energy 54 rests on supporting members 52. The supporting members 52 and the scissors lift 56 may be placed on any suitable work area, such as a table (notshown). Additional support, such as that provided by scissors lift 56, is often required for removing narrow trims since the primary source of thermal energy 54 supports the glass only under the intended path of cut 32, and in removing narrow trims, the bulk of the piece is unsupported unless additional support is provided.

As illustrated in FIGS. 5 to 8, stress modification means 50 may comprise a secondary source of thermal energy 58 which is positioned adjacent to a major surface 60 that faces away from the primary source of thermal energy 54.

In the preferred embodiment of the present invention, the secondary source of thermal energy 58 comprises an infrared line heater having a heat source 64 and an elliptical reflector 66. Heat source 64 is placed at a first focus of the elliptical reflector 66 with the second focus being at major surface 60 and along the intended path of cut 32. Secondary source of thermal energy 58 is similar to the thermal sources disclosed in the above-mentioned Dear applications. The only difference between the primary source of thermal energy 54 and the secondary source 58is that the primary source 54 may extend for the entire length of the intended path of cut 32, while secondary source 58 only extends for a length of about 2 to 4 inches along the intended path of cut 32 in an area adjacent to back edge 40.

It is important to note that the stress modification means 50 0f the present invention is not limited to a thermal source. For example, if a bending moment is applied about the intended path of cut adjacent to back edge 40, it is possible to modify the stress profile in a similar manner. Care must be taken, however, to insure that the major surface of the piece of glass facing thermal source 54 is not placed in tension.

It is also possible to use thermal sources other than the one illustrated, however, it has been found that unless the secondary source of thermal energy concentrates the heat at back edge 40 along the intended path of cut, major surface 60 is not placed in compression about the intended path of cut at the back edge 40. For

example, if one heats the general area about the intended path 32 at the back edge 40, the flare becomes more severe adjacent this back edge. It is conceivable that cold material, such as dry ice, placed adjacent to, but not on, the intended path, adjacent to back edge 40 on major surface 60, would suitably modify the stress profile.

In operation, an edge nick 70 is first applied to front edge 41 at the intended path of cut 32. This puts a defeet in the front edge 41 which serves as a starting point for the fracture when the glass is heated. If edge nicks are placed at both the front edge 41 and the back edge 40, fractures often run from both edge nicks and these fractures do not meet to form a smooth cut edge. Piece of glass is then placed on primary source of thermal energy 54 and scissors lift 56 so that the intended path of cut 32 is aligned with primary source 54 in the manner taught in the above-mentioned Dear applications. The secondary source 58 is placed on the piece of glass 30 so that it is aligned with the intended path of cut 32 adjacent to back edge 40. Primary source 54 and secondary source 58 are then activated to concentrate thermal energy along the intended path of cut.

According to one embodiment of the present invention, one may use the thermal-fracturing techniques taught in U.S. Application Ser. No. 66,941. In thermal fracturing, glass 30 is heated along the intended path of cut so that a tensile stress in excess of approximately 1,000 pounds per square inch is created at approximately the center of the piece of glass to fracture the glass. The fracture begins at the edge nick 70 and runs along the intended path of cut to back edge 40.

According to another embodiment of the present invention, one may use the thermal-scoring/mechanicalsnapping techniques taught in U.S. Application Ser. No. 66,940. In thermal-scoring/mechanical-snapping, glass 30 is heated along the intended path of cut and then snapped mechanically before a tensile stress of 1,000 pounds per square inch is created within the glass thickness. In both cases, trims may be removed from a piece of glass leaving edges that are smooth, strong, straight, perpendicular and without flare.

As previously pointed out, the above-mentioned Dear applications set forth in detail the dimensions and operating characteristics of the infrared line heater used to thermally cut glass sheets. Since the present invention utilizes the same line heater as a primary source of thermal energy, the dimensions and characteristics will not be repeated herein. A 6-inch infrared line heater may be utilized as the stress modification means. Dimensionally, it is identical with the primary source, except that the primary source is longer for static cuts. If a 6-inch infrared line heater is utilized adjacent to back edge as a secondary source of thermal energy to modify the stress profile of the piece 30 at back edge 40, cutting time is reduced by about 30 percent in static cutting, and cutting speeds may be increased by about 30 percent in dynamic cutting. For example, consider cutting a 3-inch trim from a piece of 54-inch clear float glass that is 12 inches by 24 inches. Using a fracture-initiation score, if a 25-inch infrared line heater of the type described in the abovementioned Dear applications is positioned about a major surface of the piece of glass along the intended path of cut and operated at 600 volts to provide a heat flux of 153 watts per lineal inch, it will take approximately 16 seconds for the glass to fracture. If, in addition to the above, a 6-inch infrared line heater of the type described in the above-mentioned Dear applications is positioned opposite the major surface of the piece that faces away from the 25-inch line heater, such that approximately 4 inches of the 6-inch line heater overlaps the back edge, and the 6-inch line heater is operated at 144 volts to provide a heat flux of 143 watts per lineal inch, the cutting time is reduced to approximately 10 seconds.

I claim:

l. A method. of cutting a piece of glass along an intended path of cut comprising the steps of:

a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece,

b. providing a means for modifying the stress profile at an edge of said piece about. said intended path of cut,

0. activating said source to create the stress profile and a thermal score on the major surface of said piece,

d. activating said means to modify the stress profile at said edge, and

e. applying a bending moment about the thermal score to sever said piece.

2. A method of cutting apiece of glass along an intended path of cut comprising the steps of;

a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece,

b. providing a means for modifying the stress profile at a back edge of said piece about said intended path of cut,

c. activating said source and said means to create a thermal score on said piece, and

d. applying a bending moment about the thermal score to sever said piece.

3. A method of cutting a piece of glass as defined in claim 2 further characterized in that a fractureinitiation score is placed on said piece at said intended path at a front edge of said piece before said source is activated.

4. A method of cutting a piece of glass as defined in claim 2 further characterized in that a fractureinitiation score is placed on said piece at said intended path at a front edge of said piece before said bending moment is applied.

5. An apparatus for cutting a piece of glass along an intended path of cut comprising:

a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece,

b. means for modifying the stress profile at an edge of said piece about said intended path of cut,

c. means for activating said primary source to create the stress profile and a thermal score on the major surface of said piece,

d. means for activating said first-mentioned means to modify the stress profile at said edge, and

e. means for applying a bending moment about the thermal score to sever said piece.

6. An apparatus for cutting a piece of glass along an intended path of cut comprising:

a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within said piece,

b. means for modifying the stress profile at a back edge of said piece about said intended path of cut,

c. means for activating said source and said firstmentioned means to create a thermal score on said piece, and

d. means for applying a bending moment about the thermal score to sever said piece.

7. An apparatus for cutting a piece of glass as defined in claim 6 wherein said means for modifying said stress profile is a thermal means.

8. An apparatus for cutting a piece of glass as defined in claim 7 wherein said thermal means comprises an infrared line heater.

9. An apparatus for cutting a piece of glass as defined in claim 8 wherein said line heater comprises a heat source and a reflector for focusing heat from said heat source on said path at said back edge to place a major surface of said piece, opposite said first-mentioned major surface, in compression at said back edge about said path.

10. A method of cutting a piece of glass along an intended path of cut comprising the steps of;

a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece,

b. providing a means for modifying the stress profile at an edge of said piece about said intended path of cut, and

c. activating said primary source to create the stress profile while activating said means to modify the stress profile at said edge to sever said piece.

11. A method for cutting a piece of glass as defined in claim 10 further characterized in that a fractureinitiation score is placed on said piece at said intended path at an edge of said piece that intersects said path, before said source is activated.

12. An apparatus for cutting a piece of glass along an intended path of cut comprising:

a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece,

b. means for modifying the stress profile at an edge of said piece about said intended path of cut, and

0. means for activating said source and said firstmentioned means to sever said piece.

13. An apparatus for cutting a piece of glass as defined in claim 12 wherein said means for modifying said stress profile is a thermal means.

14. An apparatus for cutting a piece of glass as defined in claim 13 wherein said thermal means comprises an infrared line heater.

15. An apparatus for cutting a piece of glass as defined in claim 13 wherein said line heater comprises a heat source and a reflector for focusing heat from said source on said path at said edge to place a major surface of said piece, opposite said first-mentioned major surface, in compression at said edge about said path. 

1. A method of cutting a piece of glass along an intended path of cut comprising the steps of: a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece, b. providing a means for modifying the stress profile at an edge of said piece about said intended path of cut, c. activating said source to create the stress profile and a thermal score on the major surface of said piece, d. activating said means to modify the stress profile at said edge, and e. applying a bending moment about the thermal score to sever said piece.
 2. A method of cutting a piece of glass along an intended path of cut comprising the steps of; a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece, b. providing a means for modifying the stress profile at a back edge of said piece about said intended path of cut, c. activating said source and said means to create a thermal score on said piece, and d. applying a bending moment abouT the thermal score to sever said piece.
 3. A method of cutting a piece of glass as defined in claim 2 further characterized in that a fracture-initiation score is placed on said piece at said intended path at a front edge of said piece before said source is activated.
 4. A method of cutting a piece of glass as defined in claim 2 further characterized in that a fracture-initiation score is placed on said piece at said intended path at a front edge of said piece before said bending moment is applied.
 5. An apparatus for cutting a piece of glass along an intended path of cut comprising: a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece, b. means for modifying the stress profile at an edge of said piece about said intended path of cut, c. means for activating said primary source to create the stress profile and a thermal score on the major surface of said piece, d. means for activating said first-mentioned means to modify the stress profile at said edge, and e. means for applying a bending moment about the thermal score to sever said piece.
 6. An apparatus for cutting a piece of glass along an intended path of cut comprising: a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within said piece, b. means for modifying the stress profile at a back edge of said piece about said intended path of cut, c. means for activating said source and said first-mentioned means to create a thermal score on said piece, and d. means for applying a bending moment about the thermal score to sever said piece.
 7. An apparatus for cutting a piece of glass as defined in claim 6 wherein said means for modifying said stress profile is a thermal means.
 8. An apparatus for cutting a piece of glass as defined in claim 7 wherein said thermal means comprises an infrared line heater.
 9. An apparatus for cutting a piece of glass as defined in claim 8 wherein said line heater comprises a heat source and a reflector for focusing heat from said heat source on said path at said back edge to place a major surface of said piece, opposite said first-mentioned major surface, in compression at said back edge about said path.
 10. A method of cutting a piece of glass along an intended path of cut comprising the steps of; a. providing a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece, b. providing a means for modifying the stress profile at an edge of said piece about said intended path of cut, and c. activating said primary source to create the stress profile while activating said means to modify the stress profile at said edge to sever said piece.
 11. A method for cutting a piece of glass as defined in claim 10 further characterized in that a fracture-initiation score is placed on said piece at said intended path at an edge of said piece that intersects said path, before said source is activated.
 12. An apparatus for cutting a piece of glass along an intended path of cut comprising: a. a source of thermal energy adjacent to the intended path of cut and opposite a major surface of said piece, said source being capable of creating a stress profile within the piece, b. means for modifying the stress profile at an edge of said piece about said intended path of cut, and c. means for activating said source and said first-mentioned means to sever said piece.
 13. An apparatus for cutting a piece of glass as defined in claim 12 wherein said means for modifying said stress profile is a thermal means.
 14. An apparatus for cutting a piece of glass as defined in claim 13 wherein said thermal means comprises an infrared line heater.
 15. An apparatus fOr cutting a piece of glass as defined in claim 13 wherein said line heater comprises a heat source and a reflector for focusing heat from said source on said path at said edge to place a major surface of said piece, opposite said first-mentioned major surface, in compression at said edge about said path. 